The worn-sear typically present when older weapons double and triple will eventually give you a weapon that will fire if it's dropped, bumped hard, or "just feels like it".
It's also never apparent when it will do it's automatic-fire routine. You might fire hundreds of rounds before it occurs, or one. A buddy of mine bought a Model 1917 Savage in .380 ACP. Neat little critter, but it tended to double and triple after about thirty rounds. With a small weapon, it's hard to shoot accurately when you never knew just how many rounds would fire at a time. Once ot twice, it stopped because it was out of ammunition.
Some states, like Maryland, charged an annual fee for the possession of Machineguns. When we moved, it was $10.00 per year. Single fee for one, or fifty, weapons. Due in June of the year. Maryland was actually friendly towards the owners of automatic weapons. You went to the closest State Police Barracks with your paperwork, paid $35.00 for your fingerprint cards, and they mailed you the results in about two weeks. The paperwork, when it arrived, was complete. You dropped in your photo, and your check, and mailed it to BATFE in Chicago. Because the MSP had already done a background, and a NICS, it seemed to help with the processing time.
When the paperwork returned, you picked up the weapon. No additional STATE paperwork was necessary. Just a 4473. This obviated the mandatory 7 day wait, and the application process that the libs had shoved down our throats.
Georgia is also quite friendly to such weaponry. It just requires hunting down your Chief LEO, and heading to the jail for fingerprints.